Senate Majority Leader Harry Reid is threatening to push the button on the "nuclear option" -- changing Senate rules so that only a simple majority, not 60 votes, is required to vote on presidential nominees.

Reid said Republican obstruction of President Barack Obama's picks gives him no choice but to change Senate rules. He plans to bring this change up for a vote on Tuesday.

"We shouldn't be waiting around here for months and months to get a vote on a nomination," Reid said during remarks on the Senate floor this morning.

But Republicans see labor unions' fingerprints all over Reid's trigger. Unions have been urging Reid to go nuclear in order to get Obama's five nominees for the National Labor Relations Board confirmed. If none of these nominees are confirmed by the end of August, the NLRB would lack a quorum and wouldn't be able to make rulings on labor disputes. That would leave workers without crucial protections, unions contend.

Business groups have complained the NLRB has pursued a pro-union agenda under Obama.

But that's not the argument Republicans are using in their opposition to Obama's NLRB nominees. They contend three of the president's choices served on the NLRB illegally because Obama used his power to make recess appointments to put them there -- at a time when the Senate technically wasn't in recess. A federal appeals court ruled the Senate wasn't in recess when these appointments were made, and therefore they were invalid. The U.S. Supreme Court agreed to review this case, which was brought by a business that argued the NLRB lacked a quorum when it ruled against it. The high court's ruling could affect hundreds of rulings issued by the NLRB since these recess appointments were made.

Republicans argue that the three NLRB nominees who they say served on the board illegally should not be confirmed by the Senate. They're willing to vote on the president's other two nominees, as well as his choices to lead the Department of Labor and the Environmental Protection Agency, said Senate Minority Leader Mitch McConnell, R-Ky.

"Senate Democrats are getting ready to do permanent damage to this body in order to confirm three unconstitutionally appointed nominees by a simple majority vote," he said.

Republicans contend the proposed rule change would weaken the Senate's "advise and consent" role on presidential nominees, and turn the Senate into something like the House, where the minority party has little say on anything.

"It's a sad day for the Senate," McConnell said.

Democrats may regret this rule change when a future election costs them their majority status, Republicans said.

Reid, however, said Republican obstruction of Obama's nominees goes back long before the NLRB nominees. The American people are sick of this gridlock, he said.

"We're going to go ahead and do what's good for the country," he said.

Reid also downplayed the significance of changing the filibuster rule for presidential nominees (which would not apply to judges). He said the Senate has changed its rules 18 times since 1977.

Plus, he noted that McConnell hadn't challenged the qualifications of Obama's NLRB nominees, two of whom are Republicans.

"He just argues the president's timing was not just quite right," Reid said.